1. Field of the Invention
This invention relates to a polymer composition comprising an acrylate rubber substrate which is grafted with a vinyl aromatic monomer and an unsaturated nitrile monomer and optionally one or more compatible comonomers. More specifically the invention relates to a grafted acrylate rubber substrate wherein the rubber is a copolymer of butyl acrylate (BA) and a nitrile monomer. The resulting polymer exhibits improved Izod impact strength over similar compositions wherein the butyl acrylate rubber substrate does not contain a nitrile comonomer. The claimed compositions are useful as molding and extrusion compounds.
2. Description of Related Art
Acrylate rubber polymers grafted with styrene and acrylonitrile (ASA polymers) are well known in the art.
U.S. Pat. No. 4,224,419 to Swoboda et al. teaches an ASA polymer which uses a bimodal butyl acrylate substrate. At column 5, lines 5-10 and column 6, lines 64-67 Swoboda teaches using "additional monomers" in the butyl acrylate rubber substrate.
U.S. Pat. No. 4,753,988 to Henton et al. is an improvement on the Swoboda ASA polymer. At column 2, line 35 to column 3, line 4 and claims 2, 3 and 4 Henton teaches using 0 to 20% by weight of a comonomer such as acrylonitrile (AN) or methyl methacrylate (MMA) in the butyl acrylate rubber substrate.
U.S. Pat. No. 4,880,875 to Wassmuth et al. is another improvement on the Swoboda ASA polymer. At column 3, lines 15-51 Wassmuth teaches using 0 to 30% by weight, preferably 20 to 30% by weight of a comonomer, e.g. S, AN or MMA in the BA rubber substrate.
U.S. Pat. No. 5,120,788 to Seitz et al. teaches up to 50% by weight of a comonomer in butyl acrylate rubber substrate in column 3, lines 17-22.
U.S. Pat. No. 5,252,666 to Seitz et al. teaches use of 0.1 to 20% by weight of a hydroxyl alkyl acrylate comonomer in butyl acrylate rubber substrate to obtain improved notched izod impact and lower molding temperature.